Much more than water
- Health Partners Research Foundation and the Departments of Ophthalmology, HealthPartners Medical Group Regions Hospital, 640 Jackson Street, St Paul, MN 55101, USA and the University of Minnesota, Minneapolis, Minnesota, USA
The belief that the tear film is aqueous based and the ocular surface changes seen in Sjögren’s syndrome are due to desiccation, cause eye care practitioners to water the dry eye. Studies show the tear film is dominated by mucin and not water.1 2 It is not a 7–10 μm thin film, but a 30–35 μm thick mucin gel. Bicarbonate may be critical to forming this gel as it is in forming the bicarbonate mucin gel that protects the stomach from autodigestion.3 The hallmark of the aqueous deficient dry eye, rose bengal staining of the conjunctiva, is not produced by desiccated cells, but is due to a deficiency in the protective mucin gel.4
The first major innovation in the treatment of the dry eye seen in Sjögren’s syndrome was the introduction of preservative-free artificial tears. Although the absence of preservatives allowed frequent topical application, the improvement seen in these severe dry eyes was more the result of the elimination of toxic preservatives …
